There are two types of meetings lawmakers can hold: formal and informal.

Formal sessions are normally reserved for discussion, debate, and voting on major issues. But during the first year of a legislative cycle, formal business must be wrapped up by the third Wednesday in November.

During the second year of a cycle — such as this year — formal session can be held through the last day in July.

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During periods when formal sessions are barred, lawmakers can resort to “informals” to get things done.

Informals tend to have sparse attendance and are generally reserved for voting on measures that are noncontroversial, of relatively minor importance, or both. Think bridge names and liquor licenses.

A key reason for that: In an informal session, a measure is not allowed to pass if even a single legislator present voices an objection.

But all that is required for lawmakers to enter informals and pass a measure is to have at least one Republican and at least one Democrat present.

Passing a controversial measure via an informal session has happened before, but it is challenging because it typically requires a lot of behind-the-scenes jockeying.

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In one example, in late 2002, lawmakers passed a bill that shielded outgoing Governor Jane Swift from personal liability in a lawsuit filed by a member of the Massachusetts Turnpike Authority. That provision was passed during an informal session that was not televised — two days after Christmas, when only a few lawmakers were in the chamber.

It’s not uncommon for informal sessions to be fairly busy at this time of year, as lawmakers scurry to pass measures before the close of the legislative cycle. But seemingly straightforward measures passed during informal sessions have caused headaches later on.

In December 2014, lawmakers in an informal session quietly passed a law requiring drivers to turn their headlights on in the daytime when the weather impaired visibility.

The measure wasn’t controversial until after it took effect and people noticed that a violation came with a costly insurance surcharge on top of a $5 ticket. The surcharge was later removed during a formal session.

Jim O’Sullivan of the Globe staff contributed to this report. Material from the Associated Press was used in this report. Matt Rocheleau can be reached at matthew.rocheleau@globe.com. Follow him on Twitter @mrochele